A transceiver includes a transmit/receive terminal, a receiver input terminal, a plurality of impedance transformation networks coupled in series, a plurality of power amplifiers, and a controller. Each impedance transformation network has first and second ports. The impedance transformation networks include at least one selectable impedance transformation network having a resonant mode and a termination mode. The power amplifiers have outputs respectively coupled to the second ports of corresponding ones of the impedance transformation networks. In a receive mode, the controller selects the resonant mode for each selectable impedance transformation network and disables all power amplifiers. In a transmit mode, the controller enables a selected power amplifier and selects the resonant mode of any upstream selectable impedance transformation network, and selects the termination mode of a downstream selectable impedance transformation network.
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17. A method comprising:
in a first transmit mode:
providing a transmit signal at a first power level; and
coupling said transmit signal to a transmit/receive terminal using a first portion of a scalable impedance network having a first characteristic impedance looking from an input of said first portion toward said transmit/receive terminal,
in a second transmit mode:
providing said transmit signal at a second power level; and
coupling said transmit signal to said transmit/receive terminal using a second portion of said scalable impedance network having a second characteristic impedance looking from an input of said second portion toward said transmit/receive terminal, wherein said second characteristic impedance is higher than said first characteristic impedance, and
in a receive mode:
receiving a signal from said transmit/receive terminal using all of said scalable impedance network.
12. A transceiver comprising:
a terminal;
a plurality of impedance transformation networks forming a scalable impedance transformation network comprising:
a first impedance transformation network having a first port coupled to said terminal and a second port; and
a second impedance transformation network having a first port coupled to said second port of said first impedance transformation network, and a second port and having a resonant mode and a termination mode;
a plurality of power amplifiers comprising:
a first power amplifier coupled to said second port of said first impedance transformation network; and
a second power amplifier coupled to said second port of said second impedance transformation network; and
a controller that:
in a first transmit mode provides a transmit signal to said terminal using said first power amplifier while placing said second impedance transformation network in said termination mode; and
in a second transmit mode provides said transmit signal to said terminal using said second power amplifier while placing said second impedance transformation network in said resonant mode.
1. A transceiver comprising:
a transmit/receive terminal;
a receiver input terminal;
a plurality of impedance transformation networks coupled in series, each having a first port and a second port wherein said first port of a first impedance transformation network is coupled to said transmit/receive terminal and said second port of a last impedance transformation network is coupled to said receiver input terminal, said plurality of impedance transformation networks including at least one selectable impedance transformation network having a resonant mode and a termination mode;
a plurality of power amplifiers having outputs respectively coupled to said second ports of corresponding ones of said plurality of impedance transformation networks; and
a controller that in a receive mode selects said resonant mode for each of said at least one selectable impedance transformation network and disables all of said plurality of power amplifiers, and in a transmit mode enables a selected one of said plurality of power amplifiers and selects said resonant mode of any of said at least one selectable impedance transformation network coupled between an output of said selected one of said plurality of power amplifiers and said transmit/receive terminal, and selects said termination mode of a first of said at least one selectable impedance transformation network coupled between an output of said selected one of said plurality of power amplifiers and said receiver input terminal.
2. The transceiver of
a first node, a second node, a third node, and a fourth node node;
a first impedance element coupled between said first and third nodes;
a second impedance element coupled between said second and fourth nodes;
a third impedance element having a first terminal coupled to said first node, and a second terminal;
a fourth impedance element having a first terminal, and a second terminal coupled to said second node;
a fifth impedance element coupled between said third and fourth nodes;
a first switch for coupling said second terminal of said third impedance element to said first terminal of said fourth impedance element in response to a complement of a select signal; and
a second switch for coupling said third node to said fourth node in response to said select signal.
3. The transceiver of
4. The transceiver of
5. The transceiver of
6. The transceiver of
7. The transceiver of
8. The transceiver of
9. The transceiver of
a receiver coupled to said receiver input terminal; and
a transmitter coupled to inputs of said plurality of selectively enabled power amplifiers.
10. The transceiver of
11. The transceiver of
13. The transceiver of
14. The transceiver of
a receiver coupled to said second port of said second impedance transformation network,
wherein in a receive mode said controller disables all of said plurality of power amplifiers and selects said resonant mode for said second impedance transformation network.
15. The transceiver of
said plurality of impedance transformation networks further comprises a third impedance transformation network having a first port coupled to said second port of said second impedance transformation network, and a second port, and having said resonant mode and said termination mode; and
said plurality of power amplifiers further comprises a third power amplifier coupled to said second port of said third impedance transformation network,
wherein:
in said second transmit mode said controller further places said third impedance transformation network in said termination mode; and
in a third transmit mode said controller provides said transmit signal to said terminal using said third power amplifier while placing said second and third impedance transformation networks in said resonant mode.
16. The transceiver of
18. The method of
in either said first transmit mode or said second transmit mode:
terminating said transmit signal looking from an input of said first and second portions toward a receiver input terminal.
19. The method of
in either said first transmit mode or said second transmit mode:
shorting first and second differential inputs of said receiver input terminal.
20. The method of
in said receive mode:
converting a voltage at a receiver input terminal into a current.
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This application is a division of application Ser. No. 14/558,173, filed Dec. 2, 214, entitled “Transceiver Suitable for Multiple Power Level Operation and Method Therefor,” invented by the inventors hereof and assigned to the assignee hereof.
The present disclosure relates generally to radio frequency (RF) transceivers, and more particularly to front-end circuits for RF transceivers.
RF transceivers are used in a variety of modern electronics, such as smartphones, digital radios, modems, routers, printers, and internet gateways. A variety of communication standards have been recently introduced to use over-the-air RF transmission and reception capabilities for relatively short distances, including near-field communication (NFC) having a distance of about 10 centimeters, personal area networks operative from 10 to 100 meters using a protocols such as “ZigBee”, “Bluetooth” and Bluetooth low energy (BTLE), and wireless local area networks such as “WiFi” having a maximum distance that varies based on conditions but under ideal conditions has been measured at over 300 meters. These standards are designed for particular purposes and generally have different power and signaling requirements. However many electronic products now support multiple ones of these standards, and providing separate circuitry for each standard increases product cost. Moreover it is difficult to design low cost, reliable transceivers using a common antenna that provide acceptable characteristics for both transmission and reception, such as appropriate transmit power level and acceptable noise figure (NF) for reception.
The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings, in which:
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.
In one form, a transceiver comprises a transmit/receive terminal, a receiver input terminal, a plurality of impedance transformation networks, a plurality of power amplifiers, and a controller. The plurality of impedance transformation networks are coupled in series. Each impedance transformation network has a first port and a second port wherein the first port of a first impedance transformation network is coupled to the transmit/receive terminal and the second port of a last impedance transformation network is coupled to the receiver input terminal. The plurality of impedance transformation networks includes at least one selectable impedance transformation network having a resonant mode and a termination mode. The plurality of power amplifiers have outputs respectively coupled to the second ports of corresponding ones of the plurality of impedance transformation networks. In a receive mode, the controller selects the resonant mode for each of the at least one selectable impedance transformation network and disables all of the plurality of power amplifiers. In a transmit mode, the controller enables a selected one of the plurality of power amplifiers and selects the resonant mode of any of the at least one selectable impedance transformation network that is coupled between an output of the selected one of the plurality of power amplifiers and the transmit/receive terminal, and selects the termination mode of a first of the at least one selectable impedance transformation network coupled between an output of the selected one of the plurality of power amplifiers and the receiver input terminal.
In another form, a transceiver comprises a terminal, plurality of impedance transformation networks, a plurality of power amplifiers, and a controller. The plurality of impedance transformation networks forms a scalable impedance transformation network and includes first and second impedance transformation networks. The first impedance transformation network has a first port coupled to the terminal and a second port. The second impedance transformation network has a first port coupled to the second port of the first impedance transformation network, and a second port and having a resonant mode and a termination mode. The plurality of power amplifiers includes a first power amplifier coupled to the second port of the first impedance transformation network, and a second power amplifier coupled to the second power of the second impedance transformation network. In a first transmit mode, the controller provides a transmit signal to the terminal using the first power amplifier while placing the second impedance transformation network in the termination mode. In a second transmit mode, the controller provides the transmit signal to the terminal using the second power amplifier while placing the second impedance transformation network in the resonant mode.
In yet another form, a method includes a first transmit mode, a second transmit mode, and a receive mode. In the first transmit mode, a transmit signal is provided at a first power level, and the transmit signal is coupled to a transmit/receive terminal using a first portion of a scalable impedance network having a first characteristic impedance looking from an input of the first portion toward the transmit/receive terminal. In the second transmit mode, the transmit signal is provided at a second power level, the transmit signal is coupled to a transmit/receive terminal using a second portion of the scalable impedance network having a second characteristic impedance looking from an input of the second portion toward the transmit/receive terminal. The second characteristic impedance is higher than the first characteristic impedance. In the receive mode, a signal from the transmit/receive terminal is received using all of the scalable impedance network.
In operation, transceiver front-end circuit 100 operates in a receive mode and a transmit mode. In the receive mode, signals RFOUT+ and RFOUT− are grounded. LNA 130 is operational and provides a differential signal between RFIN+ and RFIN− to further receiver circuitry, not shown in
In the transmit mode, receiver circuitry including LNA 130 is inactive, and power amplifier 140 is active. Power amplifier 140 receives and amplifies a differential signal between RFOUT+ and RFOut+ to provide a differential signal at a desired power level to transformer 120. Transistors 142 and 144 are cascode connected to provide isolation from the output (secondary winding of the transformer to the input RFOUT+ and RFOUT− (in
For example, output power is given by Equation [1] below:
in which RP is the differential impedance seen by the power amplifier looking into transformer 120. For example, if PDISS is +20 dBm and VDD=3 volts, then RP=100Ω. This relationship implies that for a given value of power supply voltage VDD, a higher transmit power requires a lower value for RP.
However there are problems with this front-end architecture. First, a high value of VDD causes a larger input voltage swing on the inputs to LNA 130. For example if VDD=3 volts, the inputs of LNA 130 see a 6-volt peak-to-peak signal swing, which becomes a reliability problem because it can cause gate rupture when transceiver front-end circuit 100 is implemented using low voltage CMOS technology. Moreover it is not feasible to use high-voltage transistors in place of low-voltage CMOS transistors in the LNA because of their poor unity-gain current frequency (Ft) and consequently large input capacitance and poorer bandwidth at the internal cascode nodes.
Second, the noise figure (NF) of LNA 130 is given by the equation:
in which Gm is the transconductance of LNA 130. Based on this equation for a given Gm, NF is inversely related to RP and to achieve a lower NF, RP needs to be higher. However this relationship creates a tradeoff in selecting a value for RP between higher transmit power (requiring smaller RP) and lower NF for better reception quality (which requires larger RP).
Third, different communication standards such as Zigbee and BTLE specify different transmit power levels. Thus selection of a value for RP (where RP is the impedance looking into the secondary winding of the transformer) for one transmit power level may degrade the power efficiency while operating a different transmit power level, for a given VDD.
In operation, transceiver 200 provides transmission and reception of RF signals over a single transmit/receive terminal 220 using a common antenna 210. It operates in both a transmit mode and a receive mode.
In the transmit mode, transceiver 200 supports multiple sub-modes by selecting particular ones of power amplifiers 250 based on the selected power requirement. ITNs 230 form a scalable impedance network between transmit/receive terminal 220 and receiver input terminal 240. The second terminal of each ITN forms a tap in which an impedance looking into any given tap toward transmit/receive terminal 220 is smaller than an impedance looking into a subsequent tap, if any. For example as shown in
Controller 280 provides a set of ENABLE SIGNALS to enable the power amplifier corresponding to the selected power specification, and disables the other power amplifiers. Controller 280 also provides a set of SELECT SIGNALS to place ITNs 234 through 236 into one of two modes based on the tap connected corresponding to the selected power amplifier. The first mode for ITNs 232-236 is known as the resonant mode in which the ITN adds a series impedance to the prior impedance. The second mode is known as the termination mode in which the ITN connects the terminals of its second port together to terminate the signal in the direction from transmit/receive terminal 220 toward receiver 260. Controller 280 provides the SELECT SIGNALS to place all “upstream” ITNs (i.e. toward antenna 210) in the resonant mode, and all “downstream” ITNs (i.e. away from antenna 210) in the termination mode. Thus in the transmit mode, controller 280 shorts the terminals of the second port of any downstream ITNs, eliminating the large signal swing on the input terminals of LNA 262.
In the receive mode, controller 280 provides all ENABLE SIGNALS in an inactive state. Controller 280 also provides all SELECT SIGNALS to select the resonant mode for all ITNs in ITNs 230.
Transceiver 200 solves the previously-mentioned problems associated with transceiver front-end circuit 100 of
The structures of ITNs that can be used for ITN 232, and ITNs 234 and 236, will now be described.
Impedance transformation network 400 further includes impedance elements 410, 420, 430, 440, and 450, and switches 460 and 470. Impedance element 410 is connected between node 401 and node 403 and has an impedance labeled “Za”. Impedance element 420 is connected between node 402 and node 404 and has impedance Za. Impedance element 430 has a first terminal connected to node 401, and a second terminal and has impedance Za. Impedance element 440 has a first terminal, and a second terminal connected to node 402, and has impedance Za. Impedance element 450 is connected between nodes 403 and 404 and has an impedance labeled “Zb”. Switch 460 has a first terminal connected to the second terminal of impedance element 430, a second terminal connected to the first terminal of impedance element 440, and a control terminal for receiving a control signal labeled “
Impedance transformation network 400 operates in the resonant mode when Si=0 and
As shown in
Note that
Thus a transceiver has been described that operates using a scalable impedance transformation network that in a transmit mode allows multiple transmit power levels but in a receive mode sees relatively high impedance for good NF. In addition it operates reliably when fabricated using low voltage CMOS manufacturing processes by reducing or eliminating the voltage swing on the receiver input during transmit mode. Moreover all components except the antenna can be implemented cheaply on a single integrated circuit using available low voltage CMOS manufacturing processes.
The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments that fall within the true scope of the claims. For example, a transceiver can be built according to the principles described above for an arbitrary number N of different power levels, in which N is an integer greater than or equal to 2. Moreover the impedance transformation networks can have impedances that vary according to the supported power levels and can be implemented using capacitors and inductors fabricated on a single integrated circuit die, or with two die using integrated passive device techniques and mounted in the same integrated circuit package. The input circuit of the receiver can be a LNA as shown, or another circuit such as a mixer. The power amplifiers, switches, LNAs, mixers, and other active circuit components can be made using different transistor types, such as N-channel MOS transistors, P-channel MOS transistors, or various combinations of the two.
Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.
Rafi, Aslamali A., Kummaraguntla, Ravi
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